One species with a disjunct distribution or two with convergent evolution? Taxonomy of two South American garlics

Abstract

The establishment of species boundaries has been a difficult task for biologists since the beginning of classifications. Within South American Allioideae (= Alliaceae), the delimitation of genera and species has long been a major challenge. Consequently, species‐level nomenclature in these groups has been difficult to elucidate. Ipheion and Tristagma are two closely related South American genera for which the delimitation and circumscription of several species continue to be unclear. Tristagma sessile, a species inhabiting the Andes and the Coast Range in Chile, and Ipheion recurvifolium, a species native to Uruguay only found close to sea level, have been considered as one species with an intracontinental disjunct distribution. The divergent habitats and distributions of these taxa have stirred the question of whether they are a single species. The present study aims to elucidate the evolutionary relationships and status of the Chilean and Pampean taxa. We also analysed the name Tristagma leichtlinii, which has long been a source of confusion. Based on their phylogenetic relationships, geographical distributions, flowering periods, and DNA content, we conclude that the two taxa are different species and assignable to separate genera. We propose that the morphological similarity of Ipheion recurvifolium and Tristagma sessile, amply corroborated in this study, might be the sum of shared synapomorphies (between Ipheion and Tristagma) and convergent features. We update the biogeographic history of the two genera and propose that similar pollinators might underpin the convergence in floral traits. We outline the differences among genera and species, present a taxonomic review with a new lectotype and consider the conservation status of the studied species.

Genomic, karyological and morphological changes of South American garlics (Ipheion) provide insights into mechanisms of speciation in the Pampean region

“…Even though I. recurvifolium exhibits floral similarities to Tristagma sessile (Phil.) Traub, this is more likely to be a result of convergent evolution of pollination strategies (Sassone et al, 2021). Our results support a unique history for I. tweedieanum and I. recurvifolium and we found no evidence of a hybrid origin or support for a shared genetic background with Tristagma sessile (Figure 2).…”

“…Moreover, in addition to the habitat differences, the flowers of I. recurvifolium bear a tube and style significantly longer than the other two species (Figure S1a,c; Table S2), suggesting this species is pollinated by different insects, probably Sphingidae (Lepidoptera; Sassone et al, 2021). Shifts in phenology and/or habitat between species would maximize individual fitness by increasing floral visitation, which can explain the lack of interspecific hybrids in nature (Sassone & Giussani, personal observation).…”

“…Different cultivars are characterized by a significant variation in flower colour (Castillo, 1986). I. recurvifolium (previously circumscribed as I. sessile, see Sassone et al, 2021) is also cultivated in Argentina and the UK, although is not as commonly used as ornamental.…”

Extracting Quantitative Information from Images Taken in the Wild: A Case Study of Two Vicariants of the Ophrys aveyronensis Species Complex

“…Natural patterns of phenotypic variation are not always congruent with patterns of genetic variation and/or patterns of spatial distribution of species. On the one hand, empirical biogeographic studies have shown that individuals from allopatric populations sometimes appear as phenotypically homogeneous across disjunct geographic ranges, whereas, on the other hand, a careful examination of sympatric individuals sometimes reveals the existence of phenotypically similar but phylogenetically different taxa (i.e., the so-called "cryptic lineages") [1][2][3]. Although different eco-evolutionary scenarios involving recent vicariance, dispersal, or biological introduction, incipient divergence in sympatry, secondary contact, and/or phenotypic convergence may be invoked to explain such overall phenotypic similarity, a question remains: are we sure that these individuals cannot be distinguished based on their phenotypes?…”

“…[2,4]. Identifying even a few phenotypic traits involved in the phenotypic differentiation may at the same time inform taxonomy and give insights into the ecological and evolutionary mechanisms leading to the observed geographic and/or genetic differentiation [3,5]. Recent advances in image-based phenotyping offer new opportunities to capture phenotypic complexity [6] and, therefore, to identify new phenotypic traits to distinguish groups of individuals and better understand the eco-evolutionary causes of phenotypic differentiation.…”